1. Field of the Invention
This invention generally relates to digital communications and, more particularly, to a system and method for maintaining a valid communication link with a destination node, by automatically sending an alarm-condition signal in the event that a receive channel is corrupted.
2. Description of the Related Art
In conventional analog communications, a receiver's gain is set to a maximum level in the event that an incoming signal cannot be detected. Some receivers have an adjustable squelch that determines the maximum gain level. In the case of a two-way radio, the familiar static/hiss sound heard by a user is associated with a receiver with an open squelch (maximum gain). The static/hiss sound is an indicator to the user that no signal is being received, or the receive signal is below the noise floor.
Conventional digital systems do not operate using the concept of squelch. In one simple case, received data is decoded or demodulated, and presented, regardless of the bit error rate (BER). If the data is to be retransmitted, the retransmitted signal is likewise full of errors. Other systems retransmit the received signal in a traffic channel, along with an error signal (e.g., BER) in an overhead channel. Other systems may shut down the traffic channel if there are too may received errors. Digital communications systems do not conventionally maintain a valid data link once the data to be transmitted becomes corrupted.
It would be advantageous if a digital communication system could transmit the digital equivalent of a squelch signal, in the event that received channel information is corrupted, to ensure that the two link ends maintain a common clock domain.
It would be advantageous if a digital communication system could send an alarm signal in a transmit traffic channel, to act as a digital equivalent to a squelch, which notifies communicate link nodes of transmission problems.